The present invention relates to the treatment of obstructions or abnormal tissue, within body passages, particularly but not exclusively blood vessels.
The human body is composed of a variety of types of passages, including blood vessels, intestines, urinary passages, etc. which may be the site of abnormal growths or deposits which create obstructions. Since such obstructions interfere with normal body functioning, and can frequently be life threatening, considerable research has been devoted to techniques for removing them from the affected body passage.
For example, in the case of blood vessels, and particularly arteries, it is not uncommon for clots or plaque to form on the vessel wall and to grow to such an extent as to substantially impede, if not totally prevent, blood flow through the artery. Techniques which are in use, or have been proposed, for dealing with such obstructions include bypass surgery, angioplasty techniques, in which the vessel is mechanically dilated at the site of the obstruction in order to reopen the blood flow path, and a variety of techniques for mechanically removing the obstruction from the vessel wall. All of the techniques developed or proposed thus far have been found to possess one drawback or another.
Balloon angioplasty is frequently employed when an artery is partially blocked because it represents an essentially non-surgical technique for achieving an immediate opening of the blood flow path. In many cases, the portion of the artery which is subjected to balloon angioplasty will remain open for a substantial period of time. On the other hand, it is a quite common occurrence for a new blockage to develop in the location which has been subjected to balloon angioplasty. It appears that the new blockage occurs as a response of the blood vessel tissue to the mechanical damage resulting from the balloon angioplasty procedure. Specifically, balloon angioplasty will frequently, if not invariably, effect some tearing of the blood vessel wall and the ensuing healing process involves the development of smooth muscle tissue which tends to create a new blockage.
It is known that the materials which commonly form obstructions in blood vessels are capable of being dissolved by various chemical agents, but that such agents cannot be introduced into the circulatory system in a concentration sufficient to achieve an effective dissolution action. However, it has been recently proposed to confine such agents to the region of an obstruction in order to enable a sufficient concentration of the agent to be established in a medium which is in contact with the obstruction, without exposing the remainder of the circulatory system to the dissolution agent, or at least to unacceptably high concentrations of that agent. Such a technique is the subject, for example, U.S. Pat. No. 5,222,941.